This invention relates to advantageous ligand systems and fluxional metallocene catalyst components made therefrom which are useful in producing olefin polymers and especially elastomeric propylene polymers.
Recently, a new class of metallocene-based catalyst systems has been described based upon unbridged substituted indenyl structures which have been identified as xe2x80x9cfluxional.xe2x80x9d These systems are described in the Waymouth et al. U.S. Pat. No. 5,594,080, incorporated by reference herein. Fluxional metallocene components are based on aryl 2-substituted indenyl ligands that ore formed into a metallocene which incorporates a transition metal, including Group 4 (IUPAC Periodic System) metals such as titanium, zirconium, and hafnium. These fluxional catalysts in combination with an anionic co-catalyst such as methylaluminoxane or a borate or borane compound, may be used to produce olefin polymers including elastomeric propylene polymers.
U.S. Pat. No. 5,594,080 describes a series of fluxional catalyst systems which include catalysts prepared from 2-phenylindenyl ligands which form elastomeric propylene polymers. A theory set forth for these Waymouth catalyst systems is that the 2-aryl substituted indenyl ligands rotate about the central metal to form catalysts with differing symmetry. Characteristics of polymerized olefins will depend upon the rotational symmetry state of the catalyst. For example, propylene Will polymerize into isotactic segments when the catalyst is in a xe2x80x9cracxe2x80x9d rotational symmetry state, while atactic segments will be formed while the catalyst is in a xe2x80x9cmesoxe2x80x9d rotational symmetry state. Certain Waymouth-type metallocene structures are described in Published PCT Application WO 98/57996, incorporated by reference herein, which has common inventors to this application.
As reported by Waymouth et al., elastomeric polypropylene may be formed by fluxional catalyst systems. However, polymerization activities of the catalyst systems reported by Waymouth et al. remain modest and more active catalysts are needed for commercially-acceptable processes. Further, desirable properties for elastomeric polypropylene include reasonably high molecular weights as indicated by a low melt flow rate (MFR) and suitably high polymer crystallinities which are dependent on isotacticity measured by 13C NMR, e.g. isotactic pentad content (% m4).
Fluxional catalyst systems have produced a variety xe2x80x9cblockyxe2x80x9d olefin polymers with advantageous polymer characteristics. A blocky polymer will contain segments of differing compositional microstructures. An example of a blocky polymer is a propylene polymer containing blocks of atactic and isotactic regions which may show plastomeric or elastomeric properties. Other examples of blocky polymers may contain co-monomers within the segments. The broad class of fluxional catalysts and polymers related to this invention are described in Waymouth et al. U.S. Pat. No. 5,594,080. However, in order to make production of polymers made from fluxional catalysts commercially practicable, catalysts with higher polymerization activities coupled with production of suitable polymers are needed. The catalysts described in this invention generally are more active compared to catalysts made with structurally similar ligands under comparable conditions.
A ligand useful to form a metallocene olefin polymerization catalyst comprises: 
wherein at least R3 and R4 are substituents having at least a bulk of a t-butyl group and, optionally, wherein R1 or R2 may be a bulky substituent group.
The present invention is an advantageous metallocene catalyst system based on a ligand system containing bulky substituents at least at the 3 and 5 phenyl positions as shown below: 
These bulky substituents are based on tertiary carbon or silicon. Typically these tertiary atoms are substituted with C1-C4 alkyl or substituted (with such as a halide) alkyl. The preferable bulky substituents are t-butyl and trimethylsilyl (TMS). A bulky substituent according to this invention has a spatial bulk (as indicated by steric or van der Waals repulsions) at least as large as a tertiary butyl group.
Optionally, bulky substituents may be placed at the 5 and 6 indenyl positions as shown above. Thus, the ligand systems of this invention contain at least one bulky substituent for groups R3 and R4, and optionally for R1 and R2.
Also, R1 and R2 may be connected to form a cycloaliphatic ring system containing 4 to 20 carbon atoms containing tertiary alpha carbon atoms as exemplified by 2-(3,5-di-t-butylphenyl)-5,5,8,8 tetramethyl-5,6,7,8-tetrahydrobenz(f)indene as shown below: 
In more preferable ligands, both R3 and R4 are bulky and comprise t-butyl or trimethylsilyl (TMS).
Specific examples of ligands include R3 and R4 are t-butyl or TMS; R1 and R2 are t-butyl or TMS and R3 and R4 are t-butyl or TMS; R3 and R4 are t-butyl or TMS and R1 and R2 are connected to form a cyclohexyl with quaternary alpha carbon atoms; R1 is t-butyl or TMS and R3 and R4 are t-butyl or TMS; and R1 and R2 are t-butyl or TMS and R3 is t-butyl or TMS.
Bis metallocene catalyst components of this invention, especially bis hafnium and zirconium metallocene components, generally show higher olefin polymerization activity than metallocene components formed from structurally similar ligands. Further, polymerizations showing this increased activity typically produce polyolefins with sufficiently low melt flow rates (MFR as measured by ASTM D1238, Condition L) such that hydrogen or other agent may be used to control molecular weight to a useful melt flow range without the polymer transforming into an unsuitable low molecular weight product. Typically polymers formed from the catalysts of this invention without hydrogen have MFR""s from below 1 to about 2. Addition of a molecular weight control agent may increase these polymers to a melt flow rate typically from about 1 up to about 100, typically about 1 to 35, and preferably about 2 to about 25. Further, propylene polymer crystallinities are dependent on isotacticity, a measure of which is percent of pentad and longer isotactic runs, measured by percent m4 (% m4), as determined by 13C nmr techniques. Therefore, isotacticity (m4) is generally indicative of polymer properties. The relationship between polymer properties, crystallinity and isotacticity depends on the polymer structure (blockiness) and propagation statistics. Based on typical materials of this invention, an m4 content less than about 20% typically is an amorphorus gum elastomer which will draw to high elongation, but is very soft and inelastic and exhibits poor recovery and little or no tensile hardening at high strain ( greater than 500%) unless the molecular weight is extremely high. A polymer with an m4 content of about 20-25% to 40-45% typically is elastomeric and will exhibit recovery ( greater than 80%), hardening at high strain no yielding, and uniform specimen deformation. A polymer with an m4% of about 20 to 25% is borderline between amorphous and elastomeric. A polymer with an m4 content of about 40-45% to about 50-55% typically is plastomeric and will exhibit low to medium recovery (70-80%), strain hardening, low to no yielding, and some non-uniformity of specimen deformation. A polymer with an m4% of about 40 to 45% is borderline between elastomeric and plastomeric. A polymer with an m4 content of about 55 to 80+% typically is a soft polypropylene which is plastic which yields and draws. A polymer with an m4% of about 90 to 100% usually is described as isotactic polypropylene. For propylene polymers made from catalysts of this invention, products in the elastomeric and plastomeric range are preferred; elastomeric properties may be most preferred if elastomeric characteristics are desired.
Metallocene catalyst components may be formed by known techniques. Zirconium and hafnium metallocenes are preferred and hafnium metallocenes are most preferred. The Examples disclose methods for preparing the metallocenes in high yield. Generally, metallocenes are prepared by forming the indenyl ligand followed by metallation with the metal tetrahalide to form the complex in synthetic procedures known to the art.
Appropriate cocatalysts include alkylaluminum compounds, methylaluminoxane, or modified methylaluminoxanes, as illustrated in U.S. Pat. No. 4,542,199 to Kaminsky, et al.; Ewen, J. Am. Chem. Soc., 106 (1984), p. 6355; Ewen, et al., J. Am. Chem. Soc. 109 (1987) p. 6544; Ewen, et al., J. Am. Chem. Soc. 110 (1988), p. 6255; Kaminsky, et al, Angew. Chem., Int. Ed. Eng. 24 (1985), p. 507. Other useful cocatalysts include Lewis or protic acids, such as B(C6F5)3 or (PhNMe2H)+B(C6F5)4+, which generate cationic metallocenes with compatible non-coordinating anions in the presence or absence of alkyl-aluminum compounds. Catalyst systems employing a cationic Group 4 (IUPAC Periodic Series) metallocene and compatible non-coordinating anions are described in U.S. Pat. Nos. 5,198,119, 5,198,401, and 5,223,467; Marks, et al., J. Am. Chem. Soc., 113 (1991), p. 3623; Chien, et al., J. Am. Chem. Soc., 113 (1991), p. 8570; Bochmann et al., Angew. Chem. Intl., Ed. Engl. 7 (1990), p. 780; and Teuben et al., Organometallics, 11 (1992), p. 362, and references therein; all incorporated by reference herein.
In one of many embodiments, these catalyst systems may be placed on a suitable support such as silica, alumina, or other metal oxides, magnesium halide such as MgCl2 or other supports. These catalysts can be used in the solution phase, in slurry phase, in the gas phase, or in bulk monomer. Both batch and continuous polymerizations can be carried out. Appropriate solvents for solution polymerization include liquefied monomer, and aliphatic or aromatic solvents such as toluene, benzene, hexane, heptane, diethyl ether, as well as halogenated aliphatic or aromatic solvents such as methylene chloride, chlorobenzene fluorobenzone, hexaflourobenzene or other suitable solvents. Use of liquid hydrocarbon is preferred such as hexane or heptane is preferred to avoid halogenated waste streams. Various agents can be added to control the molecular weight, including hydrogen, silanes and metal alkyls such as diethylzinc.
Polymers made according to this invention are prepared by contacting one or more olefin monomers such as ethylene, propylene, or other C4-C8 alpha-olefin, with the above-described catalyst system under suitable polymerization conditions. Such conditions include polymerization or copolymerization temperature and time, pressure(s) of the monomer(s), avoidance of contamination of catalyst, choice of polymerization or copolymerization medium in slurry processes, the use of additives to control homopolymer or copolymer molecular weights, and other conditions well known to persons skilled in the art. Production of propylene and ethylene polymers is preferred.
Typically, sufficient amounts of catalyst or catalyst component is used for the reactor system and process conditions selected. The amount of catalyst will depend upon the activity of the specific catalyst chosen.
Irrespective of the polymerization or copolymerization process employed, polymerization or copolymerization should be carried out at temperatures sufficiently high to ensure reasonable polymerization or copolymerization rates and avoid unduly long reactor residence times, but not so high as to cause catalyst deactivation or polymer degradation. Generally, temperatures range from about 0xc2x0 to about 120xc2x0 C. with a range of from about 20xc2x0 C. to about 95xc2x0 C. being preferred from the standpoint of attaining good catalyst performance and high production rates. A preferable polymerization range according to this invention is about 50xc2x0 C. to about 80xc2x0 C.
Olefin polymerization or copolymerization according to this invention is carried out at monomer pressures of about atmospheric or above. Generally, monomer pressures range from about 20 to about 600 psi (140 to 4100 kPa), although in vapor phase polymerizations or copolymerizations, monomer pressures should not be below the vapor pressure at the polymerization or copolymerization temperature of the alpha-olefin to be polymerized or copolymerized.
The polymerization or copolymerization time will generally range from about xc2xd to several hours in batch processes with corresponding average residence times in continuous processes. Polymerization or copolymerization times ranging from about 1 to about 4 hours are typical in autoclave-type reactions. In slurry processes, the polymerization or copolymerization time can be regulated as desired. Polymerization or copolymerization times ranging from about xc2xd to several hours are generally sufficient in continuous slurry processes.
Examples of gas-phase polymerization or copolymerization processes in which the catalyst or catalyst component of this invention is useful include both stirred bed reactors and fluidized bed reactor systems and are described in U.S. Pat. Nos. 3,957,448; 3,965,083; 3,971,786; 3,970,611; 4,129,701; 4,101,289; 3,652,527; and 4,003,712, all incorporated by reference herein. Typical gas-phase olefin polymerization or copolymerization reactor systems comprise at least one reactor vessel to which olefin monomer and catalyst components can be added and which contain an agitated bed of forming polymer particles. Typically, catalyst components are added together or separately through one or more valve-controlled ports in the single or first reactor vessel. Olefin monomer, typically, is provided to the reactor through a recycle gas system in which unreacted monomer removed as off-gas and fresh feed monomer are mixed and injected into the reactor vessel. A quench liquid, which can be liquid monomer, can be added to polymerizing or copolymerizing olefin through the recycle gas system in order to control temperature.
Irrespective of polymerization or copolymerization technique, polymerization or copolymerization is carried out under conditions that exclude oxygen, water, and other materials that act as catalyst poisons. Also, according to this invention, polymerization or copolymerization can be carried out in the presence of additives to control polymer or copolymer molecular weights. Hydrogen typically is employed for this purpose in a manner well known to persons of skill in the art. Although not usually required, upon completion of polymerization or copolymerization, or when it is desired to moderate or terminate polymerization or copolymerization or at least temporarily deactivate the catalyst or catalyst component of this invention, the catalyst can be contacted with water, alcohols, carbon dioxide, oxygen, acetone, or other suitable catalyst deactivators in a manner known to persons of skill in the art.
The polymerization of olefins according to this invention is carried out by contacting the olefin(s) with the catalyst systems comprising the transition metal fluxional component and in the presence of an appropriate cocatalyst, such as an aluminoxane, a Lewis acid such as B(C6F5)3, or a protic acid in the presence of a non-coordinating counterion such as B(C6F5)4xe2x88x92.
Polymer produced according to this invention may be formed into pellets by melt extrusion and chopping, which then may be used to form useful articles such as fibers, films, and other fabricated products. Polymers of this invention may be combined with effective amounts of typical polymer additives known to the art such as heat and uv stabilizers, anti-oxidants, acid scavengers, anti-stat agents, and the like.